THIS invention relates to a method and apparatus for charging an upwardly oriented hole with a pumpable material. In one application, the invention relates to a method and apparatus for charging an upwardly oriented shot hole, typically in a mine working, with a pumpable explosive.
In many types of underground mining, for example mining using the block caving technique, it is appropriate to drill shot holes upwards into the ore body of the mine from an access tunnel or other working. Depending on the type of mining these holes could be drilled parallel to each other or they could be drilled in a diverging or converging pattern. These holes then need to be charged with explosives in order to break the rock.
If charging is with ANFO it is a relatively easy process as it simply entails blow loading the ANFO into the holes with compressed air. The particles of ANFO are relatively friable which means that when the product is blow loaded the particles break up and the ANFO compacts in the hole. In the case of cartridged explosive the cartridges can be air loaded into the holes where they break and compact on hitting the toe of the hole and thus completely fill the hole and jam in place. If the hole is not excessively long the cartridges can be compacted by hand by using a charging pole to break up the cartridges.
The result is similar to that obtained with air loaded cartridges. In addition when using cartridges it is possible to use any of a variety of proprietary devices for keeping the explosive in place. These are generally made of plastic and are designed to be easy to push into the hole and to lodge therein. Due to their shape such devices are often referred to as ‘milking stools’ or ‘spiders’.
However most modern, major mining operations make use of pumpable explosives delivered from vehicle based devices often referred to as mobile manufacturing units or MMUs. In most cases the product is pumped as a non-explosive which is then mixed with an activator which causes gas bubbles to form in the product, rendering it explosive. These products are classified in the United Nations handbook on dangerous goods as Ammonium Nitrate Emulsions, suspensions or gels and are normally abbreviated ANEs. In some cases the mine will use a highly insensitive explosive with a 1.5 classification. These products are also pumpable and are often sensitized by the inclusion of glass microballoons in the formulation. Irrespective of whether the mine is using an ANE, a 1.5 explosive or any other pumpable material, the problem with an upwardly inclined shot hole is that the material is fluent and therefore has a tendency to flow out of the hole under gravity either during loading or after the hole has been filled.
Various methods are in use to stop the explosive from coming out of the hole but these all have drawbacks of one kind or another. For example, with emulsions some manufacturers incorporate a device in the end of the loading hose that causes the viscosity of the emulsion to increase dramatically as it leaves the end of the hose, with the increased viscosity acting to keep the product in the hole. At least one manufacturer adds a component to the emulsion that causes the product to become sticky such that the stickiness keeps the product in the hole.
With slurries or watergels, which in this group of products are referred to as suspensions or gels, manufacturers add a crosslinking agent to the product as it emerges from the end of the hose. This causes the product to gel or solidify in as little as ten seconds in order to retain the product in the hole.
Even with these measures a problem is that it is possible for air to find its way between the product and the wall of the hole and once this happens it is simply a matter of time before it falls out of the hole. Water running out of the hole and vibrations from the firing of adjacent shots tends to increase the likelihood of the explosive falling out.
In the above systems it is necessary to push the filling hose all the way to the end of the hole before commencing with the charging of the hole and then to withdraw the hose as the hole fills. For short holes this can be done by hand, but for long holes the process normally involves the use of a mechanical hose pusher because a long length of hose full of product can be heavy and difficult to handle. These hose pushers are expensive and if they break down for any reason significant production time could be lost.
It is potentially much simpler to fill the hole from the bottom by pumping the explosive from the collar of the hole to the upper end or toe of the hole. This requires a vent pipe to allow the air to escape as the hole fills with product. For this type of operation there are again a number of methods in use.
One such method involves the use of a solid plug with the vent pipe and filler hose passing through it. The plug may consist of two opposing wedges fitted into the hole in such a way that the pressure of the column of explosive drives the upper wedge into contact with the lower wedge, thereby expanding the wedge combination laterally into locking engagement with the wall of the hole.
However the wedges, which are destroyed in the blast, can be expensive and difficult to install properly. In addition removal of the wedges may be problematical in the event that the explosive needs to be removed from the hole for any reason.
Another known method involves the use of an inflatable ball, with filling and vent lines passing through it, to hold the product in the hole. The ball is equipped with a filling valve to allow it to be inflated with compressed air once it has been placed in the hole. Apart from the expense of the equipment, compressed air is not always available for inflating the ball.
The present invention seeks to provide an alternative method and apparatus for retaining a pumped liquid such as an explosive in an upwardly oriented hole such as a shot hole.